1. Field of the Invention
The present invention relates to an apparatus for transmitting image signals, and more particularly, to an apparatus for transmitting an N-bit red image signal, an N-bit green image signal and an N-bit blue image signal output from a computer system, clock signals indicative of frames of the image signals, enable signals indicative of the scan period and/or blank period of the image signals, vertical synchronization signals, horizontal synchronization signals and the like over an optical cable.
2. Description of the Related Art
In transmitting image signals to a relatively distant location, the use of a conventional cable causes a voltage drop in a signal being transmitted due to line resistance of the cable. Thus, line drivers for compensating for the voltage drop are necessary. Also, in the case of transmitting a parallel image signal, since multiple channels are necessary, a large amount of materials for transmission cables are required. Accordingly, an apparatus of converting a parallel image signal into a serial image signal and transmitting the same over an optical cable has been proposed.
However, when an image signal is transmitted over an optical cable, skews in received signals may occur due to a difference in transmission speeds of the respective channels, which is because the individual properties of each emitter driving circuit, each received signal amplifying circuit, each emitting element or a receiving element are not homogeneous. If the level of the skew exceeds a predetermined value, the image of the received signal cannot be reproduced properly.
To solve the above problem, it is an object of the present invention to provide an apparatus for converting a parallel image signal into a serial image signal and transmitting the same over an optical cable, wherein a difference in transmission speeds of the respective channels of the optical cable can be corrected.
To achieve the above object, the present invention includes an apparatus for transmitting over optical cables a red image signal, a green image signal, and a blue image signal output from a personal computer, a clock signal indicative of the starting points of data frames of the image signals, an enable signal indicative of scan and blank periods of the image signals, a vertical synchronization signal and a horizontal synchronization signal. The apparatus includes a reference signal generator, a parallel-to-serial converter and a light signal generator. The reference signal generator generates a reference signal having predetermined data when the blank period starts in accordance with the enable signal. The parallel-to-serial converter converts the reference signal corresponding to the blank period and the image signals corresponding to the scan periods into serial signals. The light signal generator converts the clock signal, the enable signal, the vertical synchronization signal, the horizontal synchronization signal and the serial signals output from the parallel-to-serial converter into light signals to then be incident into the optical cables.
Accordingly, since the reference signal is transmitted during the blank period, it is possible to measure a time interval between a reception point of the reference signal and that of the clock signal during each blank period. In other words, since the phase of each image signal is adjusted during each scan period, the difference in transmission speeds of the respective channels can be corrected.